Vasectomy, Not Neutering, More Effective For Feral Cat Control

Feral cats live shorter, more disease-ridden lives than the average house cat, and a new study points to a path to more effectively control and reduce feral cat populations.

According to the study published in the Journal of the American Veterinary Medical Association, giving feral cats a vasectomy or hysterectomy is a more effective method to reduce a feral colony than traditional neutering or using lethal means.

While the conventional trap-neuter-release (TNR) approach to controlling a feral cat population prevents a cat from reproducing one animal at a time, the trap-vasectomy-hysterectomy-release (TVHR) method means vasectomized males continue to produce reproductive hormones, causing them to guard females on their turf from sexually intact males.

“This opens up new conversations,” said lead study author Robert J. McCarthy, a clinical associate professor of small animal surgery at the Cummings School of Veterinary Medicine at Tufts University. “The computer model indicates that vasectomy and hysterectomy should be much more effective at reducing or eliminating feral cat populations than the traditional approach of neutering. The next step is to gather evidence on how it actually works in the field.”

Currently, the preferred method for feral cat control, neutering, involves the surgical castration or removal of a female cat’s uterus and ovaries. Neutered males become sexually inactive and are supplanted on the breeding ladder by the next most dominant male. While this method is considered a more humane option than using lethal means, capturing enough cats to effectively control the feral population can be challenging. Spayed and neutered cats also live longer, thus delaying a reduction in the population.

Study researchers found that leaving males with their testicles intact and leaving the ovaries intact by performing vasectomies and hysterectomies allows the production of reproductive hormones to continue.

“With TVHR, a male cat’s life span, sexual drive and social status aren’t altered with a vasectomy, so he’ll fend off competing males who try to intrude into his area even though he can’t actually produce offspring,” said study co-author J. Michael Reed, a professor of biology in the Tufts’ School of Arts and Sciences.

One interesting side-effect of the TVHR program is that a female cat will enter a 45-day pseudo-pregnancy period after mating with a vasectomized male, further reducing the odds of a fertile female mating with a sexually intact male, Reed said.

Using a computer model developed by Stephen H. Levine, a professor of civil and environmental engineering at Tufts, the researchers were able to compare the predicted efficacy of TVHR with that of TNR and the use of lethal means. Each computer model included a feral cat population over 6,000 days and tracked individual cats on a daily basis. New cats were added to the population as they were born and deceased ones removed.

The computer models showed that the TVHR method could cut a population of feral cats in half with an annual capture rate of just 35 percent, and could completely eliminate the colony within 11 years at the same rate. Conversely, TNR required capturing about 82 percent of the cats in order to eradicate the colony in 11 years.